In electrical double-layer capacitors, there is one using paste-like polarizing electrodes obtained by mixing activated carbon particles with electrolyte (dilute sulfuric acid, for example) for its polarizing electrodes, and there is also one using a solid polarizing electrode made of activated carbon solidified by baking or sintering and impregnated with electrolyte.
FIG. 2 is a view showing a conventional electrical double-layer capacitor using such solid polarizing electrode. In FIG. 2, numeral 1 denotes collecting electrodes, 2 solid polarizing electrodes, 3 is a separator, and 4 is a gasket.
For the collecting electrodes 1, conductive rubber is used, for example. The separator 3 has property that it allows ions to pass therethrough but not electrons, and a porous plastic, for example, is used therefor. The gasket 4 is provided to insulate the solid polarizing electrodes 2 from its surrounding members, and insulating rubber, for example, is used therefor.
FIG. 3 is a sectional plan view taken along line X--X of FIG. 2 showing the conventional double-layer capacitor. The reference marks correspond to those shown in FIG. 3.
This example has a structure that a plurality of solid polarizing electrodes 2 face each other across the separator 3, and the collecting electrodes 1 are disposed in contact with the outer surfaces of the solid polarizing electrodes 2. Subsequently each of the solid polarizing electrodes 2 is impregnated with electrolyte and the spaces between them are filled with the remainder of the electrolyte for impregnation.
The solid polarizing electrodes have a bulk density (grams per 1 cm.sup.3) of activated carbon particles (0.5.about.0.7 g/cm.sup.3) greater than those of paste-like polarizing electrodes. Hence its capacitance is greater. The solid polarizing electrode is easier to handle because of its solidity, having advantages such as a high operativity in manufacturing.
An electrical double-layer capacitor, such as this, has an internal resistance due to the resistance existing in parts where the collecting electrodes 1 are in contact with the solid polarizing electrodes 2, and the resistance of the solid polarizing electrodes 2 themselves. It is desirable for a capacitor to have its internal resistance as small as possible. However, as far as the solid polarizing electrodes 2 are employed, the resistance that the solid polarizing electrodes 2 themselves possess must be accepted.
Therefore, in order to reduce the internal resistance, it is necessary to minimize the resistance in the above parts. Therefore, the contacts between the collecting electrodes 1 and the solid polarizing electrodes 2 should be improved by application of pressure using a mechanical force exerted from the outside of the collecting electrodes 1 (from both the top and bottom thereof in FIG. 2) by caulking the edge of a metal casing (not shown), or by another method.
As a literature regarding an electrical double-layer capacitor using solid polarizing electrodes, Japanese Patent Publication No. 24100/1979 is an example.